Various mechanisms have hitherto been designed containing an input shaft for receiving input of rotational drive force and an output shaft for receiving the transmission of torque from the input shaft to intercept the transmission of load torque from the output shaft to the input shaft by generating brake torque when the load torque is applied to the output shaft.
Conventionally general irreversible mechanism of this kind has the following configuration. That is, as shown in FIG. 3, the general irreversible mechanism a1 has the configuration in which a ball ramp part a4 interposed between an input shaft a2 and an output shaft a3 converts rotational drive force of load torque applied to the output shaft a3 to an axial load, and apply this load to multi-plate brakes a5 in order to generate brake torque (See Patent Document 1, for example).
And, with such configuration, there are the following problems. That is, the problem exists that the overall length in the axial direction of the irreversible mechanism a1 including the multi-plate brakes a5 and its number of components increase because the multi-plate brakes a5 are constructed with many friction plates a6 arranged in a state that they are layered along the axial direction. Furthermore, the problem exists that the overall length of an housing a8 accommodating the input shaft a2, the output shaft a3, the friction plates a6 and so on accordingly increases and disadvantages in weight, costs, etc. of such irreversible mechanism a1 as a whole are also given because the overall length in the axial direction of the irreversible mechanism a1 is large.